\section{Yosys by example -- Advanced Synthesis}

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\sectionpage
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\begin{frame}{Overview}
This section contains 4 subsections:
\begin{itemize}
\item Using selections
\item Advanced uses of techmap
\item Coarse-grain synthesis
\item Automatic design changes
\end{itemize}
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\subsection{Using selections}

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\subsubsection{Simple selections}

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Most Yosys commands make use of the ``selection framework'' of Yosys. It can be used
to apply commands only to part of the design. For example:

\medskip
\begin{lstlisting}[xleftmargin=0.5cm, basicstyle=\ttfamily\fontsize{8pt}{10pt}\selectfont, language=ys]
delete                # will delete the whole design, but

delete foobar         # will only delete the module foobar.
\end{lstlisting}

\bigskip
The {\tt select} command can be used to create a selection for subsequent
commands. For example:

\medskip
\begin{lstlisting}[xleftmargin=0.5cm, basicstyle=\ttfamily\fontsize{8pt}{10pt}\selectfont, language=ys]
select foobar         # select the module foobar
delete                # delete selected objects
select -clear         # reset selection (select whole design)
\end{lstlisting}
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\subsubsection{Selection by object name}

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The easiest way to select objects is by object name. This is usually only done
in synthesis scripts that are hand-tailored for a specific design.

\bigskip
\begin{lstlisting}[xleftmargin=0.5cm, basicstyle=\ttfamily\fontsize{8pt}{10pt}\selectfont, language=ys]
select foobar         # select module foobar
select foo*           # select all modules whose names start with foo
select foo*/bar*      # select all objects matching bar* from modules matching foo*
select */clk          # select objects named clk from all modules
\end{lstlisting}
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\subsubsection{Module and design context}

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Commands can be executed in {\it module\/} or {\it design\/} context. Until now all
commands have been executed in design context. The {\tt cd} command can be used
to switch to module context.

\bigskip
In module context all commands only effect the active module. Objects in the module
are selected without the {\tt <module\_name>/} prefix. For example:

\bigskip
\begin{lstlisting}[xleftmargin=0.5cm, basicstyle=\ttfamily\fontsize{8pt}{10pt}\selectfont, language=ys]
cd foo                # switch to module foo
delete bar            # delete object foo/bar

cd mycpu              # switch to module mycpu
dump reg_*            # print details on all objects whose names start with reg_

cd ..                 # switch back to design
\end{lstlisting}

\bigskip
Note: Most synthesis script never switch to module context. But it is a very powerful
tool for interactive design investigation.
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\subsubsection{Selecting by object property or type}

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Special pattern can be used to select by object property or type. For example:

\bigskip
\begin{lstlisting}[xleftmargin=0.5cm, basicstyle=\ttfamily\fontsize{8pt}{10pt}\selectfont, language=ys]
select w:reg_*        # select all wires whose names start with reg_
select a:foobar       # select all objects with the attribute foobar set
select a:foobar=42    # select all objects with the attribute foobar set to 42
select A:blabla       # select all module with the attribute blabla set
select foo/t:$add     # select all $add cells from the module foo
\end{lstlisting}

\bigskip
A complete list of this pattern expressions can be found in the command
reference to the {\tt select} command.
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\subsubsection{Combining selection}

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When more than one selection expression is used in one statement they are
pushed on a stack. At the final elements on the stack are combined into a union:

\medskip
\begin{lstlisting}[xleftmargin=0.5cm, basicstyle=\ttfamily\fontsize{8pt}{10pt}\selectfont, language=ys]
select t:$dff r:WIDTH>1     # all cells of type $dff and/or with a parameter WIDTH > 1
\end{lstlisting}

\bigskip
Special \%-commands can be used to combine the elements on the stack:

\medskip
\begin{lstlisting}[xleftmargin=0.5cm, basicstyle=\ttfamily\fontsize{8pt}{10pt}\selectfont, language=ys]
select t:$dff r:WIDTH>1 %i  # all cells of type $dff *AND* with a parameter WIDTH > 1
\end{lstlisting}

\medskip
\begin{block}{Examples for {\tt \%}-codes (see {\tt help select} for full list)}
{\tt \%u} \dotfill union of top two elements on stack -- pop 2, push 1 \\
{\tt \%d} \dotfill difference of top two elements on stack -- pop 2, push 1 \\
{\tt \%i} \dotfill intersection of top two elements on stack -- pop 2, push 1 \\
{\tt \%n} \dotfill inverse of top element on stack -- pop 1, push 1 \\
\end{block}
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\subsubsection{Expanding selections}

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Selections of cells and wires can be expanded along connections using {\tt \%}-codes
for selecting input cones ({\tt \%ci}), output cones ({\tt \%co}), or both ({\tt \%x}).

\medskip
\begin{lstlisting}[xleftmargin=0.5cm, basicstyle=\ttfamily\fontsize{8pt}{10pt}\selectfont, language=ys]
# select all wires that are inputs to $add cells
select t:$add %ci w:* %i
\end{lstlisting}

\bigskip
Additional constraints such as port names can be specified.

\medskip
\begin{lstlisting}[xleftmargin=0.5cm, basicstyle=\ttfamily\fontsize{8pt}{10pt}\selectfont, language=ys]
# select all wires that connect a "Q" output with a "D" input
select c:* %co:+[Q] w:* %i c:* %ci:+[D] w:* %i %i

# select the multiplexer tree that drives the signal 'state'
select state %ci*:+$mux,$pmux[A,B,Y]
\end{lstlisting}

\bigskip
See {\tt help select} for full documentation of this expressions.
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\subsubsection{Incremental selection}

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TBD
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\subsubsection{Creating selection variables}

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TBD
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\subsection{Advanced uses of techmap}

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\subsubsection{TBD}

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TBD
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\subsection{Coarse-grain synthesis}

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\subsubsection{TBD}

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TBD
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\subsection{Automatic design changes}

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\subsubsection{TBD}

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TBD
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